1. Field of the Invention
The present invention relates to an anode catalyst for a fuel cell, and a membrane-electrode assembly including the same. More particularly, the present invention relates to an anode catalyst that can save cost of a fuel cell and that has improved efficiency, and a membrane-electrode assembly including the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and a fuel such as hydrogen, or a hydrocarbon-based material such as methanol, ethanol, natural gas, and the like. The polymer electrolyte fuel cell is a clean energy source that is capable of replacing fossil fuels. It has advantages such as high power output density and energy conversion efficiency, operability at room temperature, and being small-sized and tightly sealed. Therefore, it can be applicable to a wide array of fields such as non-polluting automobiles, and electricity generation systems and portable power sources for mobile equipment, military equipment, and the like.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol as a fuel.
The polymer electrolyte fuel cell has an advantage of having a high energy density while being able to output a high amount of power, but it also has problems because there is a need to carefully handle hydrogen gas and the requirement for accessory facilities such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel gas. On the contrary, a direct oxidation fuel cell has a lower energy density than that of the polymer electrolyte fuel cell, but has the advantages of easy handling of the liquid-type fuel, a low operation temperature, and no need for additional fuel reforming processors.
In the above-mentioned fuel cell system, a stack that generates electricity substantially includes several to scores of unit cells stacked adjacent to one another, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly is composed of an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”) that are separated by a polymer electrolyte membrane.
A fuel is supplied to the anode and adsorbed on catalysts of the anode, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into the cathode via an external circuit, and the protons are transferred into the cathode through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode, and then the oxidant, protons, and electrons react on catalysts of the cathode to produce electricity along with water.
For an anode catalyst of a fuel cell, a platinum-based catalyst is generally used due to its high catalytic activity. However, the cost of this platinum-based catalyst is high and therefore research has been undertaken for another catalyst that can be substituted for the platinum-based catalyst. For example, Pd, which is relatively cheaper than platinum, can be used for an oxidation reaction catalyst of hydrogen fuels since it can be used either in the form of a supported or black type, like platinum. Therefore, Pd is considered for a substitute catalyst for platinum-based catalysts. However, catalytic activity of Pd is significantly lower than platinum and thus Pd is difficult to use as a substitute catalyst for platinum. What is needed is an improved catalyst that is both less expensive and performs well.